In DCE imaging, an MRI or CT sequence is recorded after a contrast agent (CA) has been injected intravenously. The recorded sequence consist of dynamic concentration time curves (CTC) recorded for each voxel, which shows the contrast agent induced signal (˜which can be related to relative CA concentration) in a given voxel as a function of time. Thereby, DCE imaging can be used to make a quantitative estimates of tissue perfusion and tissue blood volume, i.e. the amount of blood per unit tissue volume and per unit time that flow through the capillaries of the vascular bed of a given tissue region. These quantitative estimates of tissue perfusion metric can reveal details related the type and state of the tissue, also referred to herein as hemodynamic parameters. In particular, dynamic susceptibility contrast (DSC) MRI is an increasingly used method to characterize brain tumors and in particular gliomas. Several studies have shown that DSC-MRI can be used to improve tumor grading and further to predict patient prognosis and treatment response.
However, a number of artefacts appear in DCE imaging, two of which are the subject of the present invention.
An important step in quantitative tumor perfusion analysis is related to correction for extravascular leakage of the contrast agent into the tumor tissue. Many brain tumors result in disrupted blood-brain-barrier (BBB) causing the contrast agent to leave the intravascular space and leak into the interstitial space. This extravasation has a confounding effect on the estimations of tumor blood volume and perfusion unless corrected for
One particular mathematical correction method has become widely used is described in Boxerman et al., American Journal of Neuroradiology 27 (2006), 859-67 as well as in U.S. Pat. No. 6,807,441. The method suggested herein corrects for extravasation by assuming relaxation to be dominated by T1-shortening and then correct for leakage relative to an average first-pass pass response for the entire image slice. The method implicitly assumes that the variation in tissue MTT and delay is small relative to the slice average MTT/delay. Given the highly heterogeneous vasculature in tumor such as gliomas, MTT/delay values which deviate significantly from the mean MTT are very likely and may lead to incorrect estimations of contrast agent extravasation. This method is used as a reference method and is denoted Method I in the following.
Another method described in U.S. Pat. No. 7,567,832 and Quarles et al., Magnetic Resonance in Medicine 53 (2005), 1307-1316. A disadvantage of this approach is that a very long time series is needed to correctly identify the leakage term from the apparent residue function and further that CBV leakage correction cannot be performed directly from the residue function.
Hence, improved ways of estimating and correcting for extravascular leakage of contrast agent would be advantageous.